(1) Field of the Invention
The present invention relates to a waterproof composite sheet material. More particularly, the present invention relates to a waterproof composite sheet material useful for sails of wind surfing equipment or sail boats.
(2) Description of the Related Art
It is well known to make waterproof sheet materials for tents, sails, or cover sheets out of a fibrous sheet material and waterproof covering layers formed on one or both surfaces of the sheet material and consisting essentially of a thermoplastic resin, for example, polyvinyl chloride resin.
When the waterproof sheet material is required to be light, the covering layer is made of a polyacrylic resin or chlorosulfonated polyethylene resin.
Also, it is known to produce waterproof sheet materials for sails of wind surfing equipment or sail boats by coating or impregnating both surfaces of a fibrous sheet material with a waterproof resinous material, for example, a melamine-formaldehyde resin or polyacrylic ester resin, or by laminating waterproof thermoplastic resin films on both surfaces of a fibrous sheet material.
For example, Japanese Unexamined Patent Publication No. 58-222847, published on Dec. 24, 1983 for Toray Inc. discloses a sail laminate consisting of a biaxially drawn polyester film and at least one fibrous sheet material layer bonded to at least one surface of the polyester film with a bonding material consisting of a thermoplastic polyesterether copolymer.
Also, Japanese Unexamined Utility Model Publication (Kokai) No. 59-187436, published on Dec. 12, 1984 for Teijin Limited, discloses a sail cloth consisting essentially of a laminate of a plain weave fabric made of polyester filament warps and wefts and polyester film layers bonded to the fabric with a polyurethane resin bonding material, which laminate is characterized in that all the elongations of the fabric in the directions of the warps, the wefts and the bias under a tension of 18 kg/5 cm are 3% or less and the peeling strength of the fabric from the polyester film layer is more than 2 kg/3 cm.
However, when the conventional sheet materials are immersed in fresh water or seawater for a long period of time, it was found that the fresh water or seawater penetrated into the inside of the sheet material due to the capillarity of the fabric.
This penetration of fresh water or seawater causes the following problems.
(1) The peeling strength of the fabric layer from the polyester film layer is degraded by the penetrated fresh water or seawater. This phenomenon results in separation of the fabric layer from the film layer.
(2) When the penetrated fresh water or seawater is maintained between the fabric layer and the polyester film layer for a long period of time, the sheet material is discolored and/or mildew grows on the sheet material.
Accordingly, it is strongly desired to provide a new type of waterproof sheet material which is free from penetration of fresh water or seawater therein.